Cell Culturing
Cells generally exist as three-dimensional aggregates in the body, but in classical plate culturing, cells are cultured in a monolayer fashion with the cells attached to a vessel. Numerous reports have indicated significant differences in cell properties with different culturing environments. An alternative is suspension culturing in which cells are cultured in a liquid culturing medium, but some cells are suited for suspension culture while others are not.
The NanoCulture® Plate (NCP) developed by SCIVAX Corporation is an adhesive-type three-dimensional culturing multiplate patterned with an extracellular matrix (microspheres or microhoneycomb) on the bottom surface by nanoimprint technology. A regular repeating structure is adopted, which is quadrilateral for microspheres and hexagonal for microhoneycombs. The cells utilize this micropattern as a scaffold to actively form spheroids (numerous cells aggregated into a three-dimensional structure).
Also, there have been reports of using cell culture sheets with regular arrangements of numerous uniform superfine cellular projections (nanopillars) (“nanopillar cell culture sheets”) for culturing of three-dimensional interstitial tissue (spheroids) having a structure similar to live hepatic tissue (Takahashi et al., Tissue Engineering Part A. June 2012, Vol. 16, No. 6, p. 1983-1995).
Japanese Unexamined Patent Publication No. 2009-213421 describes a spheroid production method and spheroid production apparatus that use a honeycomb-shaped porous film (honeycomb film).
These cell culture methods are similar in that they utilize a sheet (film) having a regular repeating pattern, in that the cells grow while adhering to the sheet surface shape, and in that what are formed by the cell culturing are spheroids in which numerous cells of the same shape are aggregated into a three-dimensional state, and in this sense these methods are restricted. There has been a demand for development of a method for more convenient, more efficient and more stable culturing of cells.
Porous Polyimide Film
Polyimide is a general term for polymers containing imide bonds in the repeating unit, and usually it refers to an aromatic polyimide in which aromatic compounds are directly linked by imide bonds. An aromatic polyimide has an aromatic-aromatic conjugated structure via an imide bond, and therefore has a strong rigid molecular structure, and since imide bonds have powerful intermolecular force, it has a very high level of thermal, mechanical and chemical properties.
Porous polyimide films have been utilized in the prior art for filters, low permittivity films, and especially for battery-related purposes, such as fuel cell electrolyte membranes and the like. International Patent Publication No. WO2010/038873, Japanese Unexamined Patent Publication No. 2011-219585 and Japanese Unexamined Patent Publication No. 2011-219586 describe porous polyimide films with numerous macro-voids, having excellent permeability for gases and the like, high porosity, excellent smoothness on both surfaces, relatively high strength and, despite high porosity, also excellent resistance against compression stress in the film thickness direction.